Transformer



Patented Feb. 16, 1943 UNITED STATES PATENT OFFICE TRANSFORMER PercivalK. Ranney, Lakewood, Ohio Application March. 24, 1941, Serial No.384,836

3 Claims.

This invention relates to transformers which are adapted particularlyfor use with gaseous tubes, ignition systems and in any circuit where itis desirable to have a relatively high starting voltage and a loweroperating voltage.

A transformer heretofore in use and having a relatively high startingvoltage and a lower operating voltage has been one wherein primary andsecondary windings have been positioned on a core, with shunts betweenthe windings for regulating the secondary current. An object, therefore,of this invention is to so improve such transformer construction thatthe secondary current and heat may be sufficiently controlled,regardless of any combination of secondary short circuits, that thetotal heat generated.

will not result in failure of the transformer.

The aforesaid object is carried out in the pre-.

ferred manner by means of a magnetic and heat dissipating shield which,when added to the high induction transformer aforesaid, accomplishes thedesired features with a minimum of material, weight and space. Theinvention is hereinafter more fully described in the drawings whichillustrate several embodiments thereof, while the essential novelfeatures are summarized in the claims.

Fig. 1 is a vertical longitudinal sectionthrough the transformer; Fig. 2is a transverse section,

on the plane indicated by the line 2-2 on Fig. 1; Fig. 3 is aperspective on smaller scale of the core, coils and shields of thetransformer as ready for mounting in the case; Figs. 4 to 8 inclusiveare views similar to Fig. 2 of five differ ent modifications of theshield arrangement, and Fig. 9 is another view of the embodiment of Fig.8, being a section on the line 9-9 on Fig. 8.

In my transformer I employ aclosed or O-type of core with a primary coiland a secondary coil on each leg of the core and preferably with amagnetic shunt from one leg to the other located between the primary andsecondary windings. Such is the construction illustrated in each of theviews.

Referring first to Figs. 1, 2, and 3, 10 indicates a laminated closed orO-type core. This may be readily made up of two sets or stacks ofL-shaped stampings of thin sheet metal, the ends of the short legs Habutting the sides of the long legs of the other stack adjacent the freeend thereof. To maintain'all these laminations in position, I reversethe position of the outermost laminations so that the short legs of suchoutermost laminations may overlap the short legs of the other stackconstituting the intermediate laminations-the outermost laminations thusmaking splice plates holding the intermediate laminations in place-and Isecure all the parts together by bolts I2 extending through thelaminations, as indicated in Figs. 1 and 2.

Around the long legs of such O-core (before the two stacks are securedtogether), I place the primary and secondary windings, as shown in Fig.1; there are two primary coils designated P, and two secondary coilsdesignated S.

Between the primary and secondary coils, in the space between the twolegs of the core, I employ a metallic shunt 20. This is composed ofmagnetic laminae separated from the two legs of the core by interposednon-magnetic material 2|, providing the desired air gap.

So much of the construction as is above described is of standard orconventional form, except that by reason of the electro-magnetic andheat shielding about to be described, I am able to make the transformersmaller and lighter than usual. The shields of my invention take variousforms, as illustrated in different views hereof and will now bedescribed.

In Figs. 1, 2, and 3, 30 indicates one pair of shields, being sheets ormagnetic material bent inwardly at their ends 3| and 32 to'make astructure channel-shaped in cross section.

.These shields abut the core outside of the primary and secondarywindings, in a manner making a magnetic connection, and are retained inplace by suitable means, as for instance, the connecting wire springs 33hooking into openings in the two sheets and extending across the core.Thus the shield plates or shunts thread the magnetic circuit of thecore.

The structure described is adapted for mounting in suitable case 40 ofcomparatively narrow rectangular form open at the top and covered by adownwardly flanged cover 4|. The case is shown in Fig. 1 as carrying atone end an insulating block 50, in which both primary terminals 5| maybe mounted (one being shown in Fig. 1), and carries at its opposite endsinsulating bushings 55 carrying the two secondary terminals 56. Suitableinsulating members 50 may extend about the outside of the secondarycoils to insulate them from the shields and case.

The core, coils, insulation and magnetic shields as a unit arepreferably imbedded in compound, which fills the space between theshields, core and windings and space outside of ing through the Neonsign.

Icircuited secondary,

secondaries may be bonded or grounded to the core (as indicated .at 58in Fig. 1), and the core may be bonded or grounded to the case about tobe described, while the case in ordinary use may be grounded to theearth. Thus, there is a mid-point ground on the secondary keeping thevoltage to ground of both terminals ap proximately one-half the totalsecondary voltage.

Themagnetic shields 30 contacting with the core act as heat dissipatorstransferring some of the heat from the core by conduction into the idlespace within the filling material in the case, or they may touch thecase 40 and transfer heat directly. This enables the use .of a smallerand lighter core without the same becoming unduly hot from theelectro-magnetic action. This is a useful function of the shields, butin addition,

hey provide safety devices or shunts protecting the secondary coils fromexcessive current in case of a short-circuit. This will now bedescribed.

The two secondary coils, as heretofore stated, are mid-point grounded.Now if one of the lead lines from a secondary terminal to a Neon sign,-for instance, should happen to burn out, break or otherwise contact withthe earth, that one of p the coils from which such lead came would beshort-circuited, while the other secondary coil would be open as therewould be no circuit flow- Now in the aforesaid transformer not having myshields, such shortcircuiting of one of the secondary coils would causemore than normal current in the short hence, it would be likely to thecore.

ary, this being either additional shield members as shown in Fig, 5, orby means of two brackets 36, as shown in Fig. 6. The purpose of this isto prevent radio frequencies which may develop in the secondary loadfrom passing to the primary and, hence, to the electric light circuits,as such radio frequencies might interfere with radio reception.

In Fig. 7, I have illustrated a single U-shaped shield 31 taking theplace of the two shields 3B of Figs. 1 and 3. This shield 31 may beseparated from the bottom of the core by a nonmagnetic spacing block 38,providing a reluctance, while the free ends of the shield member engagethe other end of the core, as illustrated.

In Figs, 8 and 9, I have shown the core l5 as made of nesting laminae 15(which could be produced by spirally winding a continuous ribbon ofmetal and then cutting it into two U-shaped sections) and in that case Iprefer to employ a set of nesting shields 39 of magnetic material havingtheir inturned edges abutting the different core laminae, so that eachlamina of the shield coacts or contacts with each lamina of Thisconstruction has the advantage "'f'of providing a flux by-pass directlyfrom each burn out. If the size of the wire of the secondenough to standsuch extra curary were heavy of material in norrent there would be' awaste mal operation.

In normal operation, the shields are practically idle, but when onesecondary is shorted, sufficient flux passes through the shields so thatthe secondary short circuited current is limited to safe values. Hence,the shorted secondary is not subjected to dangerous flow of current andis not burned out even though its wire is of the size needed for normaloperation. It results that from the current limiting protection affordedby my shields, as well as from their heat dissipating function, that Ican make the transformer lighter and smaller and more compact. Thestructure may therefore be said to be midpoint shunted because theshields act as shunts for the core between the mid-point of the primarywindings and the mid-point of the secondary windings.

If desired, I may augment the action of the.

shields by the case itself, by making the case of magnetic material andarranging its top and bottom to contact with the core or nearly sobeyond the primary and secondary. This is illustrated in Figs. 2 and 3,when the core rests on' a non-magnetic plate 42 which rests on thebottom of the case, while the cover of the case substantially contactswith the top of the core. The plate 42 provides the desired reluctancein the additional by-pass furnished by the case. If

desired, the case alone might be used as the shield.

Fig. 4 shows a multiple shield 34 made up of several laminae which maycarry more flux than a single sheet of metal. Figs. 5 and 6 showarrangements of shields which may be metallic, but non-magnetic materialto coact with the core between the primary and secondlamina of the core.The shunts 25 between the coils are-arranged to extend between the two.U-shaped core portions and project toward each other, the reluctance inthe shunt path being provided by the central non-magnetic gap, as shownin Fig, 9.

It will be seen that in each of the embodiments shown, I have providedan O-type core with primary and secondary windings on the two legs withmagnetic shunts between the legs of the core located between the primaryand secondary and with my protecting shield plates on the outer sides ofthe core and windings, the shield plates having inturned portionscoacting with the core beyond the primary and the secondary. Thereluctance to the flux path provided by the shield may be controlled byits inherent magnetic inefficiency, or by its poor magnetic connectionto the core, or both, so that the shield is substantially magneticallyidle in ordinary operation. It further acts as a heat dissipator fromthe core.

In each embodiment, the shield is available, in case one of thesecondaries should become shortcircuited, to prevent burning out of suchsecondary by excessive current.

My shielding means, therefore, is always available as a heat dissipator,enabling the use of a lighter core, and is further available whenevernecessary as a protection for one short-circuited secondary, thus makingsecondaries safe without requiring heavier winding. Shunt 20 is soadjusted that a short between the high voltage ends of both secondariesis not harmful, so that the secondary current is limited in normaloperation.

I claim:

1. In a transformer, the combination of a closed circuit core, a pair ofprimary coils respectively on two legs of the core, a pair of secondarycoils respectively on the same two legs of the core, a shunt between thelegs located between the primary and secondary coils, one or more shuntsdisposed outside the coils and each comprising one or more channelshaped plates having an inturned portion at one end extending toward thecore beyond the secondary and an inturned portion at the other endextending toward the core beyond the primary, and a case containing thetransformer.

2. In a transformer, the combination of an O-type core, primary andsecondary windings on said core, a shunt extending across the corebetween the primary and secondary windings, a. case for the core andwindings, and a shunt interposed between the core and the adjacent wallof the case, the last named shunt comprising a. plate with inturnedends, the ends substantially beyond the windings and means for holdingthe last named shunt in engagement with the core.

3. In a transformer, the combination of a closed circuit core, primaryand secondary windings on 'said core, a shunt disposed between theprimary and secondary windings, a case for the core and windings, ashunt positioned on each side of the core and interposed between thecore and the adJacent wall of the case, each of said last named shuntscomprising a plate withinturned' ends, the ends substantially abuttingthe core beyond the primary and secondary windings, and means connectingthe last named shunts and holding them in engagement with the core.

PERCIVAL K. RANNEY.

